Acid-doped polyaniline is finding an increasing level of interest as a solid electrolyte for capacitors and other electronics devices. The dopants are selected from a relatively small group of acids that enhance solubility in organic solvents with a low dielectric constant, e.g., a dielectric constant of less than about 17. Acid-doped polyaniline polymers are generally considered to have no practical solubility in solvents with a dielectric constant of greater than about 17. See U.S. Pat. No. 5,567,356. The most preferred polyaniline dopant is dinonyl naphthalene sulfonic acid (DNSA).
A commercially available solution contains DNSA-doped polyaniline in a solvent mixture containing xylene, ethylene glycol monobutyl ether. Unfortunately, this solvent system is characterized by toxicity, an objectionable odor, and a solvency for inorganic salts that is sufficiently low to preclude use of the solvent for co-depositing such salts with the polymer.
It would be useful to have a solvent system that exhibited a low vapor pressure and a low toxicity.
It would be even more beneficial to have a solvent system that also had a relatively high boiling point and a relatively high dielectric constant. The higher boiling point would facilitate the use and handling of the solvent in a commercial setting. A higher dielectric constant would increase the conductivity to a point that was similar to systems using polar solvent salt systems and would be useful for some types of capacitors where an electrically conductive residue remained after solvent evaporation.
Enhanced systems for forming polyaniline-based polymer films and coatings would be particularly useful in the manufacture of capacitors. In such articles, one or more coatings of electrically conductive polyaniline-based polymer can be used as a solid electrolyte between the dielectric oxide layer and the electrodes. It would be useful to have a polyaniline-based polymer dissolution system that did not pose the problems and limitations of the former xylene solvent systems.